1. Field
The present teachings relate to resonant tanks as used in RF circuits. More particularly, the present teachings relate to methods and systems for widening the tuning range of such resonant tanks in the presence of signals with large voltage swings.
2. Description of Related Art
Resonant tanks, also known as parallel LC tanks, composed of an inductor (L) and a capacitor (C) in parallel are widely used to provide frequency selection and tuning of RF signals used in RF circuits using amplifiers and oscillators for example. Such circuits may be assembled on a printed circuit board or integrated within a die, such as for example an integrated circuit (IC). The performance of the parallel LC tank is known by its Q factor measured at a resonant frequency ω0 (angular frequency) such as a larger Q factor provides an increased performance of the tank in terms of both frequency selection and tuning. However, at resonant frequency, the parallel LC tank exhibits a finite resistance which degrades the performance of the tank. This resistance, which is in parallel to the LC tank, decreases as frequency decreases, providing a smaller load to a current feeding the LC tank and thus reducing the amplitude of the signal across the tank. Increasing the current feeding the LC tank can, to some degree, compensate for the decrease in signal amplitude but renders very wide tuning range of the LC tank more difficult.
As used in the present disclosure, the term “IC” can refer to an integrated circuit or monolithic integrated circuit composed of a set of electronic circuits on one small plate (“chip”) of semiconductor material such as silicon. An IC can also be referred to as a “chip” or a “microchip”. The set of electronic circuits within an IC are typically made of a very large number of transistors and other electronic components, which may need supply power (e.g. positive supply and negative supply) to operate.
Throughout the present disclosure, the terms “LC tank”, “parallel LC tank”, “resonant tank”, parallel resonant tank” and “tank”, are used interchangeably and refer to the same circuit comprising an inductor and a capacitor connected in parallel. The notion of an “ideal” tank and a “non-ideal” tank are described in later paragraphs of the present disclosure and need no further introduction to the skilled person.